1. Field of the Invention
The invention relates to a voltage adjusting system and method thereof, and more particularly, to a voltage adjusting system and method thereof for adjusting a driving voltage of a thermal print head (TPH).
2. Description of the Prior Art
A printing color concentration of a thermal sublimation (or thermal transfer) printer is determined by a power and printing time of a thermal print head (TPH). In other words, it is necessary to let the TPH have the same power during a printing time if the printing color concentration of the thermal sublimation printer is required to be controlled stably.
In general, the power of the TPH during the printing operation is determined by a resistance value of the TPH and an input driving voltage. Since the resistance value of the TPH has a +/−10% error range when the TPH is manufactured, the driving voltage of the TPH has to be adjusted to fit the different mean resistance values of the TPH in order to let every TPH have the same power during the printing operation.
In a conventional thermal sublimation printer, a DC-to-DC power converter and a voltage divider are coupled to a power input terminal of the TPH in order to adjust the driving voltage of the TPH, so as to enable the driving voltage of the TPH to be changed by adjusting the resistance of the voltage divider, and thereby ensure every TPH has the same or similar power during the printing operation.
The prior art utilizes a mechanical variable resistor coupled to a voltage feedback loop of the DC-to-DC power converter in order to adjust the driving voltage of the TPH. Please refer to FIG. 1. FIG. 1 shows a simplified block diagram of a voltage adjusting system 100 for adjusting the driving voltage of the TPH according to the prior art. As shown in FIG. 1, the voltage adjusting system 100 for adjusting the driving voltage of a TPH 10 includes a power converter 102 and a voltage divider 104, and the power converter 102 is coupled to a power supply 106, wherein the voltage divider 104 includes a first resistor R1, a second resistor R2, and a mechanical variable resistor VR1.
The conventional design mentioned above is only capable of adjusting the resistance of the mechanical variable resistor by hand. This means that not only is it easy to generate errors due to the adjustments being done by hand, but the production rate of the product in the production line is also reduced, and the cost of labor power is increased. In addition, if the resistance of the mechanical variable resistor is shifted from an ideal resistance due to the component aging or vibration, then the driving voltage of the TPH will be shifted accordingly. In other words, the printing color concentration of the thermal sublimation printer will be affected and result in bad printing image quality.
Other prior arts utilize a voltage regulator to control the driving voltage of the TPH, such as U.S. Pat. Nos. 4,573,058 and 5,121,135. However, both of these conventional designs have the disadvantage of high cost, and the effect of these two conventional designs is not sufficiently good.